Particle detection and embedded vision system to enhance substrate yield and throughput

ABSTRACT

The present invention generally provides an apparatus and a method for scanning a substrate in a processing system. A transmitter unit and a receiver unit are disposed on a processing system and cooperate to transmit and detect energy, respectively. The transmitter unit is positioned to transmit a signal onto the substrate surface moving between vacuum chambers, one of which is preferably a transfer chamber of a cluster tool. Features disposed on the substrate surface, which may include particles, devices, alphanumeric characters, the substrate edges, notches, etc., cause a scattering or reflection of a portion of the signal. The receiver unit is disposed to collect the scattered/reflected portion of the signal and direct the same to a processing unit. Preferably, the transmitter unit comprises a laser source and the receiver unit comprises a charged-coupled device (CCD). Preferably, the invention is integrally positioned in a processing system to allow substrate inspection during normal operation and provide real-time information.

This is a continuation of application Ser. No. 09/391,341, filed Sep. 7,1999.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

The present invention relates to a method and apparatus for detectingthe presence of defects, such as particles on a substrate surface. Moreparticularly, the invention utilizes a combination of a light source anda detector to illuminate a substrate surface and detect scattered energytherefrom.

BACKGROUND OF THE RELATED INVENTION

Semiconductor processing generally involves the deposition of materialonto and removal (“etching”) of material from substrates. Typicalprocesses include chemical vapor deposition (CVD), physical vapordeposition (PVD), etching and others. During the processing and handlingof substrates, the substrates often become contaminated by particulatesthat can lodge themselves in the features of devices formed onsubstrates. Sources of contamination include wear from mechanicalmotion, degradation of seals, contaminated gases, other contaminatedsubstrates, flaking of deposits from processing chambers, nucleation ofreactive gases, condensation during chamber pumpdown, arcing in plasmachambers and so forth. As the geometries of device features shrink, theimpact of contamination increases. Thus, current semiconductormanufacturing routinely includes inspection of substrates for particlesto identify “dirty” processes or equipment.

In general, there are two commercial methods for detecting particlecontamination on a substrate surface, one being an X-Y surface scan andanother being a rotary type scan. In each case, an actuating mechanism,or stage, is used to move a substrate relative to light sources, such aslaser diodes. FIG. 1 is a perspective view of an exemplary inspectionapparatus 10. A substrate 11 is positioned on a stage 13 capable ofmoving in an X-Y plane. In the case of a rotary type inspection device,the stage 13 is also capable of rotation about an axis. A light source12 emits light beam 14 onto the substrate 11 and irradiates the surface.The light beam 14 is focused as a spot by condenser lens 15 to define aninspected area of the substrate 11. Particles, device patterns, andother protrusions on the upper surface of the substrate 11 cause theincident light beam 14 to scatter in various directions, as shown byarrows 16, according to the light incidence angle and geometry of theprotrusions. The scattered light 16 is received by a collector lens 18and then transmitted to a detector 20 positioned in proximity to thesubstrate 11. The detector 20 is typically a Photo-Multiplier Tube(PMT), a charge-coupled device (CCD) or other light sensitive detector.The detector 20 converts the scattered light 16 into a signalcorresponding to the detected protrusions on the substrate surface. Thesignal is routed to a processing unit 22 to generate data regardingvarious parameters of interest such as the size and location of thedetected protrusions. This approach, wherein scattered light from asurface under observation is detected, is known as “Dark FieldIllumination.” Dark Field Illumination implies that only light scatteredby protrusions on the substrate surface is detected and light which ismerely reflected by the planar substrate surface is disregarded.

One disadvantage with conventional inspection systems is the prohibitivesize and cost of the systems. Current systems are typically expensivestand-alone platforms that occupy additional clean-room space. As aresult of the large area, or “footprint,” required by the stand-aloneinspection platforms, the cost of owing and operating such a system ishigh. One reason for the size of the inspection systems is the desirefor highly sensitive equipment capable of detecting sub-micronparticles. In order to achieve such sensitivity, vibration due to thevarious moving components of the platform such as the stage, whichinterfere with the inspection techniques, must be eliminated. Thus, theinspection platforms are stabilized using a massive base comprising,granite slab, for example, to minimize the effects of vibration. Toaccommodate the wide range of motion of the stage and the massive base,conventional platforms occupy a large footprint in a fabricationfacility (fab), thereby increasing the cost of operation of the overallfab.

Another problem with current inspection devices is the negative impacton throughput, or productivity. As described above, a stage moves asubstrate through an X-Y plane to position the substrate relative to thelight source. Conventional inspection platforms, such as the one in FIG.1, illuminate only a small portion, or spot, on the substrate beinginspected. The substrate is then moved repeatedly by the stage to exposethe entire surface of the substrate to the light source. Consequently,conventional platforms drastically increase overhead time associatedwith chip manufacturing. One attempt to reduce the overhead time andincrease throughput in a reticle inspection using a stage is shown inU.S. Pat. No. 5,663, 569 which utilizes optics capable of shaping thelight beam into a line, or slit, to allow for single-pass inspection.The slit dimensions are adjusted to accommodate the width of the objectunder inspection so that the object need only be scanned in a singledirection once. However, the light source is positioned to obliquelyirradiate the reticle, thereby producing a non-uniform spot pattern.Specifically, the light source is offset to one side of the reticle suchthat the reticle moves past the light source during a scan as opposed totoward or away from the light source. As a result, the light produces amore intense pattern on the portion of the reticle closer to the lightsource while a less intense pattern is produced farther away from thelight source.

Throughput is further diminished because the current inspection systemsare stand-alone platforms that require substrates to be removed from thevacuum environment of the processing system and transferred to theseparate inspection platform. Thus, production is effectively haltedduring transfer and inspection of the substrates. Further, because suchan inspection method is conducive only to periodic sampling due to thenegative impact on throughput, many contaminated substrates areprocessed before inspection and detection of problems occurs. Theproblems with substrate inspection can be compounded in cases where thesubstrates are re-distributed from a given batch making it difficult totrace the contaminating source.

It would be preferable to have an inexpensive in situ inspection methodand apparatus incorporated into existing processing systems capable ofdetecting particles on substrates. Further, the preferred inspectionapparatus should be capable of being retrofitted to existing processingsystems. The inspection apparatus should be positioned to allowinspection of each substrate before and/or after processing. Impact tothroughput should be minimized by inspecting substrates “on-the-fly”during transfer between typical processing steps without the need for aseparate inspection platform and stage.

Another problem with particle detection systems is the noise produced bychip patterns formed on substrates. During inspection by conventionalillumination techniques, the patterns act as micro-mirrors causing thelight to reflect in various directions. As a result, the patterns mayproduce misleading information, i.e., the patterns may indicate thepresence of foreign particles where none are found. In order to allowparticle detection of patterned substrates various methods and apparatushave been implemented in the art.

U.S. Pat. No. 5,463,459, entitled “Method and Apparatus for Analyzingthe State of Generation of Foreign Particles in SemiconductorFabrication Process,” provides a method of detecting foreign particleson a substrate by “eliminating” the patterns formed on the substrate.For example, corresponding portions of adjacent chips are compared todetermine differences. The chips are illuminated with a light source tocause reflection of the light which is detected by detection equipmentwhile the substrate is actuated by a conventional stage. The reflecteddistribution of light is then compared to determine the presence offoreign particles on the substrate. The portion of the resulting signalswhich are identical are erased leaving only differences in the signals.The differences are assumed to be the result of particles on thesubstrate.

While such a method can achieve relatively high resolution capable ofdetecting sub-micron particles, the necessary equipment and signalprocessing systems are complex and expensive as well as time-consumingbecause in order to produce high resolution detection long scanningtimes are needed. Further, sources of foreign particles can producelarge-scale particles, therefore, small-scale particle detection may notbe necessary in cases where catastrophic chamber failures occur. By“catastrophic” is meant flaking of material that has accumulated on thechamber surfaces.

Therefore, what is needed is a system capable of rapidly determining thecondition of a substrate in order to facilitate a subsequent substratehandling decision. That is, a preferred detection system would allow aquick decision to be made about whether an additional and more preciseparticle detection analysis is necessary. Preferably, the system wouldalso allow the substrate inspection to be performed on-the-fly andproduce real-time data on each substrate undergoing processing, ratherthan just arbitrarily selected substrates from a batch. Such a preferredsystem would maximize the system throughput and reduce operating costsby eliminating the need for time-consuming inspection of small-scaleparticles and also the cost associated therewith.

Therefore, there is a need for an integrated particle detection systemwhich allows for on-the-fly monitoring and the detection of particles ina processing system.

SUMMARY OF THE INVENTION

The present invention generally provides a particle detection apparatusin a processing system. In one aspect of the invention, a transmitterunit and a receiver unit are disposed on or near a chamber and cooperateto transmit and detect energy. The transmitter unit is positioned totransmit a signal onto a moving substrate surface. The receiver unit ispositioned to collect a scattered portion of the signal and direct thesame to a processing unit.

In another aspect of the invention, a transmitter unit and a receiverunit are disposed on a semiconductor processing system and cooperate totransmit and detect energy, respectively. The transmitter unit ispositioned to transmit a signal into a region of the processing system,such as a transfer chamber, and onto a substrate surface movingtherethrough. In one embodiment, the signal is transmitted onto asubstrate moving through a cavity of the transfer chamber and preferablybetween the transfer chamber and an adjacent vacuum chamber. A robotpreferably located in the transfer chamber or a front-end environment ofthe processing system, enables movement of the substrate. The receiverunit is disposed to collect a scattered portion of the signal and directthe same to a processing unit. Preferably, the transmitter unit and thereceiver unit are disposed in a region external to the processingsystem.

In yet another aspect of the invention, a light source and one or morecharge-coupled devices (CCD) are disposed on or near a chamber andcooperate to transmit and detect energy, respectively. The laser sourceis positioned to transmit a signal onto a moving substrate surface. TheCCD is disposed to collect a scattered portion of the signal and directthe signal to a processing unit.

In still another aspect of the invention, a signal is transmitted on asubstrate moving in a first direction between a first vacuum chamber anda second vacuum chamber of a semiconductor processing system orrotationally within the first chamber. Preferably, the first vacuumchamber is one of a transfer chamber or a front-end environment and thesecond vacuum chamber is one of a process chamber, a service chamber ora load lock chamber. A reflected portion of the signal is received by areceiver unit and subsequently directed to a processing unit forprocessing. In one embodiment, the reflected portion of the signal isreflected by particles disposed on the substrate. In another embodiment,the reflected portion of the signal is reflected by alphanumericcharacters disposed on the substrate.

In still another aspect of the invention, a signal is transmitted on asubstrate moving in a first direction between a first and second vacuumchamber of a semiconductor processing system or rotationally within thefirst chamber. Preferably, the first vacuum chamber is one of a transferchamber or a front-end environment and the second vacuum chamber is oneof a process chamber, a service chamber or a load lock chamber. Areflected portion of the signal is received by a receiver unit andsubsequently directed to a processing unit for processing. Theprocessing unit is adapted to read a computer-readable program productto generate information pertaining to the substrate. Preferably, theprogram product is adapted to provide substrate positional information,substrate reflectivity information, specular information, substratedefect information, substrate damage information, particle contaminationinformation for the substrate support member and a substrate disposedthereon, alphanumeric character information, robot behavior information,calibration information for a robot, a transmitter unit and/or areceiver unit, and any combination thereof.

In still another aspect of the invention, a method of determining thecenter and/or orientation of a substrate is provided. A substrate ispositioned in a chamber having a receiver unit and transmitter unitdisposed therein. The surface of the substrate is illuminated withradiation from the transmitter unit and an image representative of atleast an edge portion of the substrate is captured by the receiver unit.The image is analyzed to determine at least one of the center ororientation of the substrate. The substrate surface illuminated may bethe backside of the substrate or the upper surface of the substrate infacing relation to the receiver unit.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features, advantages andobjects of the present invention are attained and can be understood indetail, a more particular description of the invention, brieflysummarized above, may be had by reference to the embodiments thereofwhich are illustrated in the appended drawings.

It is to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is perspective view of a prior art inspection apparatus.

FIG. 2 is a partial perspective view of a processing system.

FIGS. 3A-C are top views of the processing system of FIG. 2 showingvarious positions of a substrate disposed on a blade during rotation ofthe blade.

FIG. 4 is a top view of the processing system of FIG. 2 showing asubstrate disposed on a blade during retraction of the blade.

FIG. 5 is a plan view of a typical cluster tool for semiconductorprocessing.

FIG. 6 is a graphical representation of specular reflections on apatterned substrate illuminated by a light source.

FIG. 7 is a comparative graphical representation of specular reflectionson patterned substrates.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention generally provides a particle detection apparatusin a processing system. A transmitter unit and a receiver unit aredisposed on or near a chamber and cooperate to transmit and detectenergy. The transmitter unit is positioned to transmit a signal onto asubstrate surface moving between vacuum chambers. Particles disposed onthe substrate surface cause a scattering of a portion of the signal. Thereceiver unit is positioned to collect and measure the scattered portionof the signal and direct the same to a processing unit. Preferably, thetransmitter unit comprises a light source and the receiver unitcomprises a charged-coupled device (CCD).

FIG. 2 is a perspective cutaway of a processing system 40 of the presentinvention comprising a transfer chamber 42 and a vacuum chamber 44mounted thereon (see FIG. 3A). The transfer chamber 42 and the vacuumchamber 44 are selectively communicable through an aperture 46 which canbe sealed by a conventional apparatus such as a slit valve door (notshown). The aperture 46 is sized to accommodate the transfer ofsubstrates therethrough. A robot 50 is centrally disposed in thetransfer chamber 42 and comprises a blade 48 coupled to the robot hub 51by frog-leg type linkage 39. The robot 50 enables rotational and radialmovement of the blade 48 along a transfer plane, thereby shuttlingsubstrates between various positions. The transfer chamber 42 and thevacuum chamber 44 are preferably components of a cluster tool 100 suchas the one shown in FIG. 5 and described in detail below. Thus, thevacuum chamber 44 may be a load lock chamber providing an interfacingchamber between a front-end environment and the transfer chamber 42,while the transfer chamber 42 provides a vacuum environment communicablewith various peripheral chambers. Alternatively, the vacuum chamber 44may be a process chamber.

As shown in FIG. 2 a transmitter unit 56 and a receiver unit 58 areexternally mounted to a lid 52 of the transfer chamber 42. Thetransmitter unit 56 includes a light source 60 and beam-shaping optics62 and is positioned to emit a signal 54 into the cavity 41 of thetransfer chamber 42 via a view port 64. The view port 64 comprises anopening formed in the lid 52 and is hermetically sealed with plate 66made of a material transparent to the signal 54 of the light source 60.In one embodiment, the plate 66 may comprise Pyrex™, for example. Inoperation, the signal 54 propagates parallel to the x-axis shown in FIG.2 and is directed onto an upper surface of a substrate 37 rotatingthrough the cavity 41 of the transfer chamber 42. The signal defines alight pattern 53 upon falling on the substrate 37. As described indetail below, the spot size of the light pattern 53 may be variedaccording the substrate size by adjusting the beam shaping optics 62 andthe position of the light source 60.

The light source 60 can be, for example, a laser source or a broadspectrum light source. In general, the light source 60 is selectedaccording scattering intensity, brightness and cost. Where a lasersource is used, the laser source is preferably operable at about 808 nm.However, other laser sources, such as 650 nm or 680 nm wavelength lasersources, may also be used.

In general, the spot size of the light pattern 53 is substantiallydetermined by the beam-shaping optics 62 and the position of thetransmitter unit 56. The beam-shaping optics 62 is selected to provide aspot size according to the dimensions of the substrate. For a 300 mmsubstrate, for example, the spot size of the light pattern 53 ispreferably at least 220 μm (width)×300 mm (length, y-axis) on the uppersurface of a substrate. Thus, in operation, the entire breadth of a 300mm substrate is exposed to the signal 54 after a single scan. However,it is believed that only 60% or more of the substrate need be exposed tothe signal 54. Typical sources of catastrophic process chambercontamination, such as flaking (also known as chamber excursions),provide hundreds of particles that may settle on the processing surfaceof a substrate. Successful particle detection requires only that aportion of the contaminants be detected to confirm the presence of acontaminated substrate. Thus, monitoring at least 60% of the processingsurface ensures a substantial probability of detecting a contaminatedsubstrate.

Referring still to FIG. 2, the receiver unit 58 is shown mounted in aview port 70 formed in the lid 52 and defines an optical path 61 towardthe substrate 37 moving through the cavity 41. The receiver unit 58 issecured above an energy transparent plate 72 made of a material selectedaccording to the operating wavelength of the signal 54 and preferablycomprises of the same material as the plate 66 disposed in view port 64.For example, where the light source 60 is a laser source operating atabout 808 nm, the material for the plates 66, 72 is selected toaccommodate a 808 nm signal. The receiver unit 58 is positioned toreceive a scattered portion 74 of the signal 54 from the substrate 37during operation. The scattered portion 64 is represented by amultiplicity of arrows oriented at various angles relative to the uppersurface of the substrate 37 and indicates the presence of anobstruction, such as particulate contamination disposed on the uppersurface of the substrate 37. A reflected portion 69 of the signal 54propagates at angle relative to the substrate 37 substantially equal tothe angle of incidence α. The reflected portion 69 represents theportion of the signal 54 substantially unobstructed upon interceptingthe upper surface of the substrate 37.

The receiver unit 58 includes an optics assembly 80, comprising one ormore lens, and a detector 82. The detector 82 of the receiver unit 58preferably comprises a charge-coupled device (CCD) line camera. A CCDline camera is a preferred detector due to its high immunity toout-of-substrate noise and its ability to provide particle coordinateson a substrate. By using a line CCD the vertical coordinate of eachdetected particle can be determined. However, while CCD detectors arepreferred, other detectors, including time delay integration (TDI)detectors, or PMT's may be used to advantage. Where a TDI detector isused the spot is adjusted to correspond to the TDI size as is known inthe art.

The foregoing description for positioning the transmitter unit 56 andreceiver unit 58 is merely illustrative and other embodiments arepossible. For instance, while FIG. 2 shows the transmitter unit 56 andthe receiver unit 58 disposed outside the cavity 41 of the transferchamber 42, in another embodiment the transmitter unit 56 and thereceiver unit 58 are positioned inside the cavity 41, and thus, undervacuum conditions. Additionally, as will be described in detail below,the invention has application other than particle detection and,therefore, can be modified accordingly.

Together, the transmitter unit 56 and the receiver unit 58 comprise anOptical Sensor Assembly (OSA). The operation of the OSA is controlled byan Electronic Processing and Interface Unit (EPI) 86. As shown in FIG.2, the EPI 86 is electrically coupled to the transmitter unit 56 by aninput cable 88 and provides command signals thereto and is electricallycoupled to the receiver unit 58 by an output cable 90 to receive outputsignals therefrom. Although the microprocessor/controller for theprocessing system 40 is preferably separate from the EPI 86, in oneembodiment the EPI 86 may serve as the control unit for the processingsystem 40, thereby eliminating the need for an additional control unit.

The EPI 86 may be operated using a computer program product comprising acomputer code, which can be run on a conventional computer. The computerprogram can be written in any conventional computer readable programminglanguage such as, for example, 68000 assembly language, C, C++, Pascalor Java. Suitable program code is entered into a single file, ormultiple files, using a conventional text editor, and stored or embodiedin a computer usable medium, such as a memory system of the computer. Ifthe entered code text is in a high level language, the code is compiled,and the resultant compiler code is then linked with an object code ofprecompiled windows library routines. To execute the linked compiledobject code, the system user invokes the object code, causing thecomputer system to load the code in memory from which the CPU reads andexecutes the code to perform the tasks identified in the program.

Upon initiation by a user, the EPI 86 continues to monitor substrateswhich enter the field of view of the receiver unit 58. If the EPI 86detects the presence of a contaminated substrate, the user may bealerted by a warning message displayed on a display unit (not shown).Additionally or alternatively, the microprocessor/controller of theprocessing system 40 can be instructed by the EPI 86 to transfer thesubstrate to a particular location for eventual disposal, cleaning orfurther inspection.

The operation of the present invention is illustrated by FIGS. 3A-C.FIGS. 3A-C are top views of the processing system 40 showing the blade48 and substrate 37 in various positions during rotation through thetransfer chamber 42. FIG. 3A shows the blade 48 immediately afterinitiating counter-clockwise rotation so that the leading edge 92 of thesubstrate 37 is positioned in the path of the signal 54. Thus, a portionof the light pattern 53, represented by the shaded area, is shownintercepting the leading edge 92 of the substrate 37. During thecontinued rotation of the blade 48, shown by FIGS. 3B-C, the lightpattern 53 scans the upper surface of the substrate 37. The lightpattern 53 illuminates particles 75 on the substrate 37 which causesscattering of the signal 54. The size of the particles 75 are typicallyin the micron range but are shown greatly exaggerated for clarity. Thescattered portion 74 of the signal 54 is then collected by the receiverunit 58. Where the detector 82 is a CCD, the scattered portion 64 isfocused by the receiver optics 80, imaged onto the elements of the CCD,converted into an electrical signal and transmitted to the EPI 86 forprocessing.

It is understood that the foregoing sequence may be performed beforeand/or after the substrate 37 undergoes a processing cycle in aprocessing chamber. For example, FIGS. 3A-C may represent a substratebeing transferred from a load lock chamber to a processing chamber.Alternatively, FIGS. 3A-C may represent a processed chamber beingtransferred to a cooldown chamber or being returned to a load lock.

While FIGS. 2 and 3A-C show the preferred positioning and operation forthe transmitter unit 56 and receiver unit 58, other embodiments may beused to advantage. In general, the transmitter unit 56 and receiver unit58 may be positioned at any point on the processing system 40 where thesignal 54 may be directed onto the upper surface of a moving substrateand scattered light may be detected by the receiver unit 58. Thus, inanother embodiment, particle detection is performed during retraction orextension of the robot 50 as describe with reference to FIG. 4. FIG. 4is a top of the processing system 40 showing the blade 48 and substrate37 disposed thereon during the retraction of the blade 48 from thevacuum chamber 44 into the transfer chamber 42 via the aperture 46. Inorder to maximize the exposed surface area of the substrate 37, thesignal 54 preferably intercepts the substrate 37 in extreme proximity tothe aperture 46 as shown in FIG. 3A. Such a positioning ensures exposureof substantially the entire upper surface of the substrate after fullretraction of the blade 48, thereby maximizing the surface area of thesubstrate 37 which is scanned by the signal 54. The shaded portion ofthe light pattern 53 indicates the portion of the signal 54 incident onthe substrate 37. As the blade 48 continues to retract, the substrate 37is moved through the path of the signal 54, thereby exposing the uppersurface of the substrate 37 to the signal 54. Particles 75 disposed onthe upper surface of the substrate 37 cause the signal 54 to scatter,shown by arrows 74. The scattered portion of the signal 54 is collectedby the receiver unit 58, converted into an electrical signal andtransmitted to the EPI 86 for processing. Upon complete retraction ofthe blade 48, the light pattern 53 is preferably radially outward of thetrailing edge 98 of the substrate 37 so that the full surface area ofthe substrate 37 has been exposed to the light pattern 53.

The embodiments shown in FIGS. 3A-C and 4 are merely illustrative. In analternative embodiment, a pair of transmitter units 56 and receiverunits 58 may be used in combination to monitor a substrate during linearmotion and rotational motion, respectively. Such an arrangement canimprove the accuracy of detection. A person skilled in the art willrecognize other embodiments. Further, while a single surface scan of thesubstrate 37 provides a high degree of accuracy relative to particledetection, additional methods may be employed to enhance detectionconfidence. For example, the robot blade 48 may be dithered, oroscillated, so that a given particle can be moved into the field of viewof another CCD detector element in the array of elements. Detection bymultiple elements provides additional certainty of the existence andlocation of the particle.

Determination of the location of a particle on the substrate is made byidentifying particular features on the substrate or blade. For example,in one embodiment the EPI may be programmed to detect the leading edge,i.e., the substrate curvature which first enters the field-of-view ofthe receiver unit, and lagging edge, i.e., the last curvature to bedetected by the receiver unit, during linear or rotational movement ofthe substrate. The substrate edges provide reference points which maythen be used to generate one of two coordinates, i.e., X and Y becausethe acquisition rate of the CCD detector is known. The acquisition raterefers to the frequency of image generation during the movement of thesubstrate in the field-of-view of the CCD detector. Preferably,consecutive image are generated so that no overlapping or missingportion of the substrate results. Thus, the processed output of the CCDdetector is a “photograph” of the complete substrate surface. Theremaining coordinate is determined by where the particle is detected onthe detector array of the CCD detector.

The present invention has particular advantages in a multi-chamberprocessing system. One exemplary multi-chamber processing systemcommonly used in the semiconductor industry, well suited for supportingthe detection apparatus described herein, is known as a cluster tool. Acluster tool is a modular system comprising multiple chambers whichperform various functions including substrate center-finding andorientation, degassing, annealing, deposition and/or etching. Themultiple chambers are mounted to a central transfer chamber which housesa robot adapted to shuttle substrates between the chambers. The transferchamber is typically maintained at a vacuum condition and provides anintermediate stage for shuttling substrates from one chamber to anotherand/or to a load lock chamber positioned at a front end of the clustertool. The centralized position of the transfer chamber provides an ideallocation for a particle detection system.

Thus, the transfer chamber 42 and the vacuum chamber 44 may each be partof a cluster tool. FIG. 5 is a plan view of a typical cluster tool 100for semiconductor processing wherein the present invention may be usedto advantage. Two such platforms are the Centura® and the Endura® bothavailable from Applied Materials, Inc., of Santa Clara, Calif. Thedetails of one such staged-vacuum substrate processing system isdisclosed in U.S. Pat. No. 5,186,718, entitled “Staged-Vacuum WaferProcessing System and Method,” Tepman et al., issued on Feb. 16, 1993,which is incorporated herein by reference. The exact arrangement andcombination of chambers may be altered for purposes of performingspecific steps of a fabrication process.

In accordance with the present invention, the cluster tool 100 generallycomprises a plurality of chambers and robots and is preferably equippedwith a microprocessor controller 102 programmed to carry out the variousprocessing methods performed in the cluster tool 100. A front-endenvironment 104 is shown positioned in selective communication with apair of load lock chambers 106. A pod loader 108 disposed in thefront-end environment 104 is capable of linear and rotational movementto shuttle cassettes of substrates between the load locks 106 and aplurality of pods 105 which are mounted on the front-end environment104. The load locks 106 provide a first vacuum interface between thefront-end environment 104 and a transfer chamber 110. Two load locks 106are provided to increase throughput by alternatively communicating withthe transfer chamber 110 and the front-end environment 104. Thus, whileone load lock 106 communicates with the transfer chamber 110, a secondload lock 106 communicates with the front-end environment 104. A robot113 is centrally disposed in the transfer chamber 110 to transfersubstrates from the load locks 106 to one of the various processingchambers 114 and service chambers 116. The processing chambers 114 mayperform any number of processes such as physical vapor deposition,chemical vapor deposition, and etching while the service chambers 116are adapted for degassing, orientation, cooldown and the like.

A number of view ports 120 provide visual access into the transferchamber 110. The view ports 120 provide suitable locations for thetransmitter unit 56 and the receiver unit 58. Arrows 122, 124 indicatepoints where inspection of a substrate may be preformed. Arrows 122represent points where the robot blade 126 is rotated and arrows 124represent points where the robot blade 126 is extended or retracted. Thetransmitter unit 56 and receiver unit 58 may be positioned in the viewports 120 accordingly as described with reference to FIGS. 2-4. Forexample, the transmitter unit 56 and receiver unit 58 may be securedabove the view port 20 in a position having field of view of the robotblade 126 entering or exiting the load lock 106. As noted above, the useof more than one transmitter unit 56 receiver unit 58 pair is alsocontemplated by the present invention. While the foregoing has beendescribed with reference a to the transmitter unit 56 and the receiverunit 58 disposed on the transfer chamber 110, the invention hasapplication at any position in the cluster tool 100 where substrate arein motion. Thus, arrows 107 indicate the movement of substrates throughother locations in the cluster tool 100 which provide additionalinspection sites.

The foregoing embodiments provide a detection apparatus and methodcapable of detecting the presence of particles on substrates on-the-flyand in situ. In situ, on-the-fly detection eliminates the need forconventional stand-alone inspection platforms comprising dedicatedactuating mechanisms such as the stage 13 shown in FIG. 1. The presentinvention-uses to advantage components typically included in anyconventional processing system, such as the robot 50 (shown in FIGS.2-4), to enable a stageless inspection system. Particle detection isperformed at various positions in a processing system during normal andnecessary operation sequences without transferring the substrates to aseparate stand-alone inspection platform, thereby minimizing the impacton throughput. Consequently, each substrate entering or exiting theprocess system can be inspected, thereby achieving a significantimprovement over prior art wherein only periodic sampling was possibledue to the negative effect on overhead time. Further, the use ofconventional features such as view ports and transfer robots facilitatesretrofitting the present invention to existing systems without the needfor expensive re-machining procedures.

For simplicity, the foregoing has been directed toward particledetection on unpatterned substrates having substantially smooth planarsurfaces. On unpatterned substrates, light from the light source 60(shown in FIG. 2) is scattered only upon striking a particle. Patternedsubstrates however include topological variances that can causescattering of incident light, thereby falsely indicating the presence ofa particle. Thus, where patterned substrates are to be examined, theinvention utilizes a unique signature produced by illuminating eachsubstrate in order to differentiate between substrates. The uniquesignature is the result of the patterns formed on the substrate. Becausethe topology due to patterns of substrates that undergo a particularprocess is substantially repetitive, the signature will be unique foreach of the substrates. Thus, the unique signature may be stored in amemory and used to compare surface conditions of substrates duringproduction.

FIG. 6 represents a scan of 3 million data points showing the specular“signature” 150 for a calibration substrate scanned according to thetechniques described above. The number of occurrences (y-axis), orreadings by the detection equipment, at a particular intensity (x-axis)are plotted. Subsequently, two different test substrates were scanned ina similar manner resulting in two separate and distinct spectralsignatures. To determine the relative conditions of the surfaces of thesubstrates, the signatures for the two test substrates were compared tothe signature 150 for the calibration substrate. The graphs 152, 154shown in FIG. 7 are the result of subtracting the number of occurrencesat a given intensity for the calibration substrate from the number ofoccurrences at the same given intensity for the two test substrates.Thus, a first graph 152 represents the difference in the recorded outputof the detection equipment between the first test substrate and thecalibration substrate and shows little variation. A second graph 154represents the difference in the recorded output of the detectionequipment between the second test substrate and the calibrationsubstrate and shows a significant variation, indicating a difference inthe surface conditions of the compared substrates.

Thus, the invention provides an efficient and effective method ofcomparing substrate surface, conditions on-the-fly in a processingsystem. In production, the invention is a viable method of determiningwhether production should be halted and a particular substrate should beexamined more carefully for contamination or defects. Only selectedsubstrates need undergo additional particle detection, therebyminimizing the impact to throughput.

In addition to particle detection, a preferred device would be capableof performing other functions typically performed in a processingchamber and inspection chamber in order to increase throughput anddecrease operating cost. In the production of devices it is necessary todetermine various characteristics of a substrate of which particlecontamination is only one. For example, substrate characteristics suchas discontinuity (the presence of fractures and other structuraldefects) are important to identify potential problems which may affectthe efficient operation of a system and lead to increased cost ofoperation due to damaged substrates. Additionally, substratecenterfinding and orientation are often necessary steps duringprocessing to generate positional information regarding substrates. Inconventional systems such procedures are performed at designatedlocations in the processing system. Thus, a substrate must be shuttledto the designated locations in order to undergo each procedure, therebydecreasing throughput. Further, because such tests are typicallyperformed only periodically on an arbitrary substrate, many substratesmay be damaged before a problem is identified.

Another situation which can cause increased processing costs is impropersubstrate routing. Occasionally, a substrate may be improperly routed toa process chamber where the processing conditions cause a volatilereaction, thereby damaging the substrate and/or the processing chamber.Because current processing systems are not equipped to preventmisrouting, the cost of operation is increased.

Thus, what is needed is a “gate-keeper” apparatus and method capable ofexamining a substrate for selected characteristics which includeparticles, orientation, centerfinding, reflectivity, substrate type,discontinuity, etc. Preferably, such an inspection can be performedprior to entry into a process chamber as well as exit from the processchamber, thereby determining real time pre- and post-processingconditions of the substrate.

Other functions routinely performed in conventional processing systemsand inspection systems include calibration of robots and the inspectionequipment. Current methods of calibration negatively impact throughputbecause the system must be halted and opened in order to perform thecalibration. A preferred processing system would allow for anintegrated, or embedded, device capable of performing these varioustasks in an integrated location and on-the-fly. Thus, the processingsystem could be further integrated and throughput can be increased. Inaddition, it would be preferable for such an integrated arrangement tobe capable of monitoring robot behavior. Robot behavior of interestincludes acceleration, speed, repeatability, stability, etc. A systemadapted to monitor such robot characteristics would provide an apparatusand method to ensure consistent robot behavior regardless of theparticular system in which the robot is implemented. Additionally, itwould be preferable for such an integrated device to determine thepresence of contamination on the robot blade which supports substratesduring transfer. The presence of such contamination indicates that thebacksides of substrates are being scratched during a substrate handlingstep. Heretofore, however, no such devices or methods has been known.

The inventors have discovered that the inspection device describedherein can be adapted to perform numerous other inventive uses needed inprocessing systems such as those just described, e.g., the determinationof selected substrate characteristics including reflectivity, substratetype, discontinuity, orientation and centerfinding, as well asperforming calibration of robots and the inspection equipment andmonitoring robot behavior. The following discussion provides variousembodiments for the present invention but is not intended to beexclusive, as those skilled in the art will readily recognize otherpossible embodiments.

In one embodiment, the invention determines the substrate type. As notedabove, the pattern of substrates provides a unique signature.Accordingly, the invention may be used to recognize substrates based ontheir pattern by scanning the substrate in the manner described aboveand transmitting the received signal to the EPI 86 for processing. Thescanned pattern is then compared to stored signatures to determine thesubstrate type. Such an application provides the ability to detect asubstrate that may have been misrouted through the system. For example,the OSA could detect and reject a substrate with photoresist which havebeen routed to a physical vapor deposition (PVD) chamber, therebypreventing potential damage to a process chamber and the substrate. Inaddition, recognition of the substrate pattern can be used toautomatically change the process recipe according to the substrate type.

Further, the invention can be used to determine process uniformity,smoothness and substrate damage or defects, such as discontinuity(structural defects of the substrate due to thermal migration, forexample, which may lead to portions of the substrate breaking off). Inoperation, the OSA and EPI 86 can be employed to generate a map of thesubstrate topology. The map can then be analyzed for texturecharacteristics such as planarity and uniformity. In addition, anysubstrate damage or defect, such as chips or fractures may be detectedand mapped. Analysis can be enhanced by use of a color CCD detector.

Another substrate characteristic which may be determined, is thereflectivity of the substrate. Information regarding reflectivity can beused to determine whether certain process conditions have beensuccessfully achieved, such as the endpoint of an etch process. Becausethe endpoint information is available in near real-time, i.e.,substantially contemporaneously with the end of the process, andproximate the processing chamber, an under-processed substrate may beimmediately returned for additional processing. Conventionally,substrates are taken to a remote location for endpoint examination. Asubsequent determination that a substrate is under-processed typicallyresults in the substrate being discarded because the time involved inreturning the substrate for additional processing is cost prohibitive.

In another embodiment, the invention provides for Optical CharacterRecognition (OCR). OCR refers to the detection and processing ofalphanumeric characters through video imaging. Substrates are oftenidentified by characters which are typically inscribed on the substratesurface. The transmitter unit 56 and the receiver unit 58 of the presentinvention provide an apparatus capable of illuminating and detecting thecharacters and then directing a signal to the EPI 86 for processing. Inoperation, a substrate is scanned in the manner described above. Duringthe scan the signal 54 will strike the characters on the substrate andbe reflected according to the geometry of the characters. As with signalreflection by patterns, described above with reference to FIG. 6, thereflection is unique to the particular arrangement and configuration ofthe characters. Thus, the resulting signal can be compared to storeddata representing previously scanned characters.

In another embodiment, the invention is used to determine a substrate'sorientation and center. Orientation and center-finding are necessary toensure proper positioning of the substrate in a chamber for particularprocesses. For example, etching involves the use of a mask to covercertain portions of the substrate surface. In order to position the maskon the appropriate portions of the substrate the orientation of thesubstrate must first be determined. The patterned surface of a properlyoriented substrate on the blade provides a unique signature (asdescribed above with reference to FIG. 6) which can be stored in acomputer system such as the EPI 86. Thus, the present invention can beused to verify the signature. As a substrate is moved into the opticalpath 61 of receiver unit 58, the receiver unit 58 determines whether thesignature is correct. If the signature is verified the conventionalorientation task can be bypassed, thereby increasing throughput.

Substrate center-finding currently employs the use of one or moresensors to determine the center of a substrate. Use of the presentinvention enables substrate center-finding capability, therebyeliminating the need for additional sensors. Additionally, thecomponents of the invention may be located outside of the vacuumenvironment of a processing system, thereby eliminating outgassingproblems associated with conventional arrangements. During operation ofthe invention, a substrate is illuminated and scanned by the OSA (i.e.,the transmitter unit 56 and the receiver unit 58) during the retraction,extension, and/or rotation of the blade. Thus, the diameter and,therefore, the center, of the substrate can be determined by the EPI 86.For example, as a substrate is moved into the path of the signal 54, theleading edge of a substrate is detected due to reflected light. Once thesubstrate passes through and beyond the signal 54, the receiver unit 58ceases to detect a signal. The time between initial detection of asignal 54 and ceasing detection is recorded. For a known robot speed,the recorded time may be used to calculate the diameter of thesubstrate. If the substrate is determined not to be centered relative toa calibrated value, an adjustment is made to the destination coordinateof the robot 50 to correct the offset. It is understood that theparticular method of calculating the substrate center is not limiting ofthe invention and people skilled in the art will recognize otherpossibilities. For example, in another embodiment, detection of theleading and lagging edges of a substrate, as described above, may beassociated with the encoder value of the robot 50 at the time ofdetection. The encoder values can then be compared to calibrated valuesfor substrates of the same diameter to determine any offset that must beaccommodated.

In another embodiment, a substrate's orientation and center can be foundwhile the substrate is positioned in a chamber, such as a cool downchamber, a degas chamber, or any other chamber of a processing systemsuch as the one shown in FIG. 5. Center finding and orientation can besimultaneously done by positioning the substrate in the field of view ofthe receiver unit 58. The receiver unit 58 may be mounted in a view portof the chamber or in any other position wherein the receiver unit 58 cancapture a substantial portion of the substrate in its field of view. Inthis manner, the chamber acts both as an area for analysis of thesubstrate as well as performing a processing function such as cooling ordegassing. As a result, analysis can proceed without affecting thethroughput of the processing system. The transmitter unit 56, ratherthan providing line-illumination as in the foregoing embodiments, isadapted to provide annular illumination about the perimeter of thesubstrate. Thus, the transmitter unit 56 may be a light-ring taking theform of a fiber optic-based light-ring, such as those commerciallyavailable from Fostee of Auburn, N.Y., and especially configured formachine vision and microscopy application. In one embodiment, thetransmitter unit 56 is disposed at an upper end of the chamber oppositethe substrate being examined. Thus, the side of the substrate facing thereceiver unit 58 may be illuminated by the transmitter unit 56.

During operation, the substrate is positioned against a uniformbackground in the chamber. The transmitter unit 56 then illuminates thesurface of the substrate and the uniform background. The illuminationprovides an image which is captured by the receiver unit 58. The imageis then transmitted to the EPI 86 for processing. Analysis of the imageby the EPI 86 is accomplished by identifying a contrast in opticaldensity. A change in contrast can be identified by comparing the opticaldensity of one area of the image to optical density of another area ofthe image. Because the substrate is positioned against a uniformbackground, analysis of the image taken by the receiver unit 58 willindicate a marked density contrast between the substrate and the uniformbackground. Thus, by analyzing contrast changes along the line orseveral lines of pixels the dimension and shape of the substrate can bedetermined. In addition, analysis of the entire image provided by thereceiver unit 58 will map the substrate perimeter indicating theposition of an orientation notch. In this manner, the center and theorientation of the substrate can be found simultaneously.

“Optical density contrast” refers to the change in contrast of the imagereceived by the ESI 86 due to illumination of varying surfaces.Different surfaces (in the case the substrate and the backgroundsurface) produce different spectral results when illuminated, asdescribed above with regard to spectral signatures. Such spectralvariations can be analyzed by the EPI 86 to determine the dimensions ofthe substrate being illuminated.

In another embodiment wherein the transmitter unit 56 is a light-ring,the transmitter unit 56 may be placed to illuminate the back side of thesubstrate. Accordingly, the transmitter unit 56 is sized to have aninner diameter slightly less than the diameter of the substrate and theouter diameter slightly greater than the diameter of the substrate. As aresult, the illuminating radiation of the transmitter unit 56 isprovided to a perimeter portion of the back side of the wafer. While thesubstrate blocks a portion of the illuminating radiation from thereceiver unit 58, a portion of the radiation outside the diameter of thesubstrate is visible to the receiver unit 58, thereby enhancing opticaldensity contrast at the substrate edge. The resulting image provides arelatively darker area corresponding to the area occupied by thesubstrate.

For contrast analysis, the receiver unit 58 is preferably atwo-dimensional CCD pixel array camera having lateral and verticalfields of view that span multiple pixels. In this manner, the acquiredimages provide multiple pixel rows and columns for quantification of asubstrate's dimensions.

A contrast analysis, as described herein, can be implemented using wellknown machine vision techniques and commercially available systems forexecuting the same. For, example, machine vision systems capable ofimplementing contrast analysis techniques are available from CognexCorporation of Matick, Mass. An example of a suitable machine visionsystem is the Cognex MVS 8000 series system, which includes a set ofPC-based machine vision hardware and software tools. With such a system,the images can be analyzed on a pixel by pixel basis to evaluate opticaldensity differences.

Accordingly, the invention provides an apparatus and method forgenerating realtime information about selected characteristics of asubstrate. Substrate inspection is preferably performed before and afterprocessing. A preferred operation of the invention may be understoodwith reference to FIG. 5. Upon transfer of a substrate from the transferchamber 110 into a process chamber 114 or service chamber 116 by therobot 113, the invention preferably operates to scan the substrate inthe manner described above. The result of the scan then producesinformation regarding substrate type, orientation, centerfinding,discontinuity, specular signature and presence of particles. Followingprocessing, these same characteristics may be determined during theretraction of the substrate from the processing or service chamber.Additionally, a determination may be made regarding the process results.For example, the reflected signal from the substrate scan may be used togenerate information on process uniformity and the process endpoint inthe manner described above.

Thus, the invention provides real or near real-time pre- andpost-processing information regarding characteristics of a substrate.Because the information is real-time an immediate cost efficientdecision can be made about how to handle the substrate. Further, becauseeach substrate may be inspected, as opposed to selected substrates froma batch, the information can be used to rectify identified problems withminimal damage to substrates and the processing environment.

In addition to inspecting a substrate, the invention is also adapted forcalibration and health monitoring. In one embodiment, the invention maybe used to calibrate the detection devices. Because the illumination anddetection optics of the invention will not be uniform, the operationmust be normalized. Normalization will be accomplished in the followingway. When the OSA (the transmitter unit 56 and the receiver unit 58) isfirst installed, a substrate will be placed upside down on a robotblade. The robot blade will then move the substrate under the receiverunit 58. During the rotation of the blade both peak-to-peak androot-mean-square (RMS) measurements are made for each element of thedetector 82. A comparison is then made between the average reading ofeach detector element to determine the correction factors necessary tonormalize the system. Subsequently, the substrate is removed and thesolid portion of the robot blade (i.e., excluding holes and edges) isthen scanned in a similar fashion. The peak-to-peak and average for eachdetector element is then compared to the normalized correction factorsto determine the blade correction factors. With the blade normalizationfactors in place, the blade can act as a resident calibration reference.Thus, the OSA can monitor the empty blade during normal operation todetermine if the optics 62, 80 are functioning properly. If the optics62, 80 are contaminated, or a detector element of the detector 82degrades, it will be detected by the foregoing background test.

Additionally, contamination disposed on the surface of the blade 48 isalso detected by the test described in the foregoing embodiment.Contamination on the blade 48 indicates that the backsides of substratesare being scratched at some point during the handling of the substrate.Thus, if contamination is detected on the blade, the system can behalted for inspection, thereby preventing further contamination to theprocessing environment.

In another embodiment, the OSA facilitates robot calibration. Theprocessing system robots, such as the transfer chamber robot 50,periodically require calibration in order to ensure proper orientationand alignment. Because the OSA is mounted at a fixed location on aprocessing system, the OSA can provide a point of reference for thetransfer chamber robot calibration. Once the blade normalization factorshave been determined, as described above, the blade features can bedetected to verify the robot position and proportional, integral anddifferential (PID) values. Sufficient variance between the detectedposition values and the calibrated position values stored by the EPI 86indicates misalignment of the blade. The misalignment can be correctedby “homing” the robot according to the stored values.

The invention also enables monitoring of robot behavior. As the robotblade is rotated through the optical path 61 (shown in FIG.2) of thereceiver unit 58, the blade edge nearest to the center of rotation willenter into the optical path 61 first. This edge will then enter thefield-of-views (FOVs) of each detector element successively at a ratewhich is determined by the blade velocity. This allows the OSA toindependently monitor the behavior of a robot including characteristicssuch as settling time, accelerations and stability can bemeasured/monitored. The collected data can be used to manually orautomatically set the PID parameters of the robot.

Various other possible applications are not discussed here in detail.For example, the invention may be used to detect the presence of asubstrate on a robot blade as well as determining whether the substrateis in a blade clamp used to secure the substrate during the movement ofthe blade. Those skilled in the art will recognize other applicationscontemplated by the present invention.

Thus, the invention facilitates the integration of numerous functionscurrently achieved by different components in a typical cluster tool.One or more single transmitter units 56 and receiver units 58advantageously positioned, such as in a transfer chamber, can performmultiple functions including center-finding, orientation, particleinspection, damage inspection, robot behavior monitoring, etc. Whilesuch tasks are currently not preformed or are performed at variouspositions of the processing platform and require dedicated equipment,the invention provides a multi-purpose apparatus capable of achieving ahigher level of system integration and reducing the system operatingcosts. By performing the substrate scanning methods described aboveon-the-fly, i.e., during necessary substrate transfer sequences, theimpact to system throughput is minimized.

Which tasks are performable on a substrate is determined by a programproduct readable by the EPI 86. Preferably, the program product issoftware readable by the EPI and includes code to generate at leastsubstrate positional information, substrate reflectivity information,specular information, substrate defect information, substrate damageinformation, particle contamination information for smooth and patternedsubstrates, particle contamination information for the robot blade,alphanumeric character information, robot behavior information,calibration information for the robot and the detection devices and anycombination thereof. It is understood that the foregoing list is merelyillustrative and other functions may be performed by the invention.

While the foregoing is directed to the preferred embodiment of thepresent invention, other and further embodiments of the invention may bedevised without departing from the basic scope thereof, and the scopethereof is determined by the claims that follow.

What is claimed is:
 1. A method for optical character recognition andparticle detection, comprising: transmitting an optical signal along afirst path into a vacuum chamber of a multi-chamber semiconductorprocessing system including at least one substrate processing chamber;moving a support member having a substrate disposed thereon from a firstposition to a second position in the vacuum chamber, wherein at least aportion of the substrate having alphanumeric characters inscribedthereon is moved through the first path, and wherein the support memberis positionable in one or more chambers of the multi-chamber processingsystem; detecting the presence of a reflected portion of the opticalsignal reflected by the alphanumeric character's geometry; generatingsignal signature information representing the alphanumeric character'sgeometry; comparing the signal signature information to a referencesignal signature information; and determining an identity of thesubstrate based on a difference between the signal signature informationand the reference signal signature information.
 2. The method of claim1, further comprising: converting the reflected portion of the opticalsignal into data representing the alphanumeric characters; and comparingthe data representing the alphanumeric characters with stored data. 3.The method of claim 1, further comprising: detecting the presence ofanother reflected portion of the optical signal reflected by particlesdisposed on the substrate surface.
 4. The method of claim 1, whereindetecting comprises receiving, at a receiver, at least some of thereflected portion of the optical signal representative of at least someof an alphanumeric character's geometry.
 5. A method for opticalcharacter recognition on a substrate, comprising: moving a substratebetween a first position and a second position in a multi-chambersemiconductor processing system; while moving the substrate,illuminating at least some portion of a substrate surface having atleast one alphanumeric character inscribed thereon; detecting areflected signal from the substrate surface representing topographicdata of the substrate surface; generating signal signature informationrepresenting the topographic data; comparing the signal signatureinformation to a reference signal signature information; and determiningthe presence of the at least one alphanumeric character based on adifference between the signal signature information and the referencesignal signature information.
 6. The method of claim 5, whereindetecting comprises receiving, at a detector unit, a portion of thereflected signal.
 7. The method of claim 5, wherein determiningcomprises generating at a process unit, data from the reflected signalrepresentative of the at least one alphanumeric character.
 8. A methodfor determining alphanumeric characters from a surface topography of asubstrate, comprising: supporting a substrate having alphanumericcharacters inscribed on a surface of the substrate, moving the substratefrom a first position to a second position within a vacuum chamber of amulti-chamber semiconductor processing system; while moving thesubstrate, illuminating a portion of the substrate surface with a signalemitted from a source; receiving a reflected portion of the signal fromthe illuminated portion of the substrate surface; generating signalsignature information representing the alphanumeric characters derivedfrom the received reflected portion of the signal; comparing the signalsignature information to a reference signal signature information; anddetermining an identity of the substrate based on a difference betweenthe signal signature information and the reference signal signatureinformation.
 9. The method of claim 8, further comprising, based on thecomparing, determining that the topographical data corresponds to atleast one of the alphanumeric characters.
 10. The method of claim 8,wherein the refected portion of the signal represents at least a portionof the signal reflected from at least one of the alphanumericcharacters.
 11. The method of claim 7, further comprising determining amatch between the generated alphanumeric character data from thereflected signal and stored alphanumeric character data match.
 12. Amethod for optical character recognition, comprising: transmitting anoptical signal along a path into a vacuum chamber of a multi-chambersemiconductor processing system including at least one substrateprocessing chamber; moving a support member having a substrate disposedthereon from a first position to a second position in the vacuumchamber, wherein at least a portion of the substrate having alphanumericcharacters inscribed thereon is moved through the path; illuminating theportion of the substrate having alphanumeric characters with the opticalsignal; detecting a presence of a reflected portion of the opticalsignal reflected by a geometry of the alphanumeric characters;generating signal signature information representing the alphanumericcharacter's geometry; comparing the signal signature information to areference signal signature information; and determining an identity ofthe substrate based on a difference between the signal signatureinformation and the reference signal signature information.
 13. Themethod of claim 12, wherein detecting the presence of the reflectedportion of the optical signal comprises receiving, at a receiver, anelectrical representation of the reflected portion of the optical signalrepresenting at least one alphanumeric character.
 14. The method ofclaim 12, further comprising detecting the presence of another reflectedportion of the optical signal reflected by particles disposed on thesubstrate surface.
 15. The method of claim 12, further comprisinggenerating a signal indicative of the detected reflected potion of theoptical signal.
 16. The method of claim 15, further comprising directingthe signal to a processing unit for signal processing.
 17. The method ofclaim 16, comparing the signal to stored alphanumeric character data todetermine a match.
 18. The method of claim 12, further comprisinggenerating, from the detected portion of the reflected optical signal,topographical data representing the alphanumeric characters.
 19. Themethod of claim 18, further comprising comparing the topographical datato stored alphanumeric character data.
 20. The method of claim 1,wherein the detecting step is performed in a front-end environment of acluster tool comprising a transfer chamber connected to the front-endenvironment by at least one load lock chamber.
 21. The method of claim1, wherein the signal signature information and reference signalsignature information are indicative of surface conditions of thesubstrate during a processing cycle.
 22. The method of claim 1, whereinthe determining step comprises determining a type of the substrate basedon the difference between the signal signature information and thereference signal signature information.
 23. The method of claim 1,wherein the determining step comprises determining an orientation of thesubstrate based on the difference between the signal signatureinformation and the reference signal signature information.